The present invention relates to a solid fine-grain dispersion of a water-insoluble photographically useful compound, and to a method for preparing the same, and further to a silver halide photographic light-sensitive material using the same.
Examples of a water-insoluble photographically useful compound include a dye image-forming coupler, a dye image-providing redox compound, an antistain agent, an antifoggant, an ultraviolet absorber, an antifading agent, a color-mix-preventing agent, a nucleating agent, a silver halide solvent, a bleach-accelerator, a developing agent, a filter dye and a precursor thereof, a dyestuff, a pigment, a sensitizing agent, a hardener, a whitening agent, a desensitizing agent, an antistatic agent, an antioxidant, a developer scavenger, a mordant, a matte (matting) agent, a development accelerator, a development inhibitor, a heat solvent, a color-tone modifier, a sliding (slipping) agent, and a polymer latex for dispersion that is used as a medium for dispersing these compounds, and a water-insoluble inorganic salt (e.g. zinc hydroxide). These water-insoluble photographically useful compounds are used in a photographic emulsion layer or another layer, as an aqueous dispersion or hydrophilic colloid dispersion of a solid fine-grain dispersion thereof. The above-described water-insoluble photographically useful compounds are described in, for example, Research Disclosure (R.D.) No. 17643, ibid. No. 18716, and ibid. No. 307105. As an example of these materials, a solid fine-grain dispersion of dyestuff is often used in a photographic emulsion layer or another layer for coloration, in order to absorb light in a specific wavelength region, and to thereby improve color reproduction and sharpness, etc. Such a colored layer is called a filter layer, an antihalation layer, a crossover-cut filter layer, or so on, depending on its purpose. Further, photographic emulsion layers have been colored in order to prevent irradiation. It is necessary for these solid fine-grain dispersions to be held (fixed) in an intended layer of the photographic coating membrane, and further for them to be sufficiently fine to the thickness of the layer.
Such a solid fine-grain dispersion of the photographically useful compound can be prepared by an ordinary method. Details of the method are described in, for example, xe2x80x9cKinosei Ganryo Oyo Gijutsu (Applied Technology of Functional Dyes), published by C. M. C. (1991).
The media dispersion method is one of ordinary methods. According to the method, a powder of a dye or a dye wetted with water or an organic solvent, which is called a wet cake, is mixed with a solvent to make a slurry, and then the resultant mixture is mechanically pulverized (ground) in the presence of dispersion media (e.g. steel balls, ceramic balls, glass beads, alumina beads, zirconia silicate beads, zirconia beads, Ottawa sand), using a known pulverizer (e.g. a ball mill, a vibration ball mill, a planetary ball mill, an agitation ball mill, an annular-type ball mill, a vertical sand mill, a roller mill, a pin-type mill, a spike mill, a co-ball mill, a caddy mill, a horizontal sand mill, an attritor).
These dispersing tools are described in, for example, xe2x80x9cKagaku Kogaku Binran (Handbook of Chemical Engineering),xe2x80x9d published by Maruzen, Revised 5th edition.
Of these media dispersion methods, the most generally used method for preparing fine grains of a photographically useful compound comprises the steps of:
successively bringing (introducing) a slurry of the compound in a milling (grinding) chamber of a dispersing machine, which chamber is filled with media,
allowing the compound to contact with the media in the grinding chamber, thereby finely pulverizing the compound, and then
separating the media from the fine-grained compound by means of a screen, a gap, a slit, a mesh, or the like. This method is excellent in such points as productivity, wide usability, attainability of small grain size of the dispersed grains, and simplicity of a manufacturing process.
However, in this method, there are such problems as that, because mechanical energy is used, the energy required to pulverize a material is large; that only a part of the applied energy is used for pulverization, and the rest, which is the majority, is given off as thermal energy; that, because machine parts and media collide with each other, thereby causing abrasion, the resultant abrasion materials get mixed in the completed dispersion, which results in deterioration of property; that, because the grain size distribution of the dispersion is wide, coarse grains are likely to remain; and that, if the supplied energy is increased so as to rapidly progress pulverization and to obtain fine grains, not only the above-described generation of heat and abrasion increase, but also mixing in of a large amount of abrasion materials takes place.
In particular, a dispersion of a photographically useful compound is coated on a support (base) as an extremely thin colloid layer. Recently, a tendency to make a thin layer and high-speed coating of the colloid layer is increasingly progressing. In this case, such problems (defects) as pin holes and unevenness due to abrasion materials that will get mixed in a colloid layer, are actualized.
Media that have been used include, for example, steel balls, Ottawa sand, glass beads, dealkali glass beads, alumina beads, zircon beads, zirconia beads, and so on. Further, the grain size thereof has been generally 0.4 mm or more.
Of these media, it is known that steel balls cause metallic abrasion materials that result in defects when a dispersion is coated on a film, and they also cause coloring and an unpreferable chemical reaction. Ottawa sand, glass beads, and dealkali beads each have not only a defect due to dispersed abrasion material but also a possibility that an alkali component or a metal salt resulting from the abrasion, decomposes or aggregates a dispersion. On the other hand, alumina beads, zircon beads, and zirconia beads are hard, and each has a high bulk density, so that a great amount of energy can be applied to the dispersion, which results in a high dispersion efficiency. However, because the machine parts of the dispersing machine are worn out, abrasion-resistant ceramic or polymeric materials have been used as a material of the machine part.
However, recently such needs as improvement of the dispersion efficiency and reduction of the dispersion grain size are increasing. Therefore, if energies are increased (a round speed and a filling rate are increased), there is such a possibility that even using hard beads, an increase in abrasion and/or generation of heat occurs, thereby raising a problem about quality and the process of production.
As a method of reducing an abrasion material, while increasing productivity, and accomplishing reduction in coarse grains by rendering the grains more fine, an attempt to make the average grain size of the media small has been made. Usually the media and a dispersion are separated from each other by means of a screen, a gap, a slit, a mesh, and so on. In these methods, there are such drawbacks that a material of the separating part tends to be worn out, and the separating part is easily plugged (clogged) as the grain size of the media becomes smaller. Further, especially when a gap is used, a space that is smaller than the grain size of the media must be maintained, so that both high processing accuracy and control accuracy are required. Accordingly, there is a problem that a large-sized dispersing machine is difficult to manufacture.
Further, a method of dispersing a material using a polymeric material or fine grains thereof, as the media, followed by separation after dispersion, is also proposed. Such a method is described in, for example, U.S. Pat. Nos. 5,500,331, 5,679,138, and 5,662,279, and, European Patent (EP) Nos. 684508A and 684519A. However, these methods have such drawbacks that both the hardness and density of the media are low, and the dispersion speed is slow, and abrasion of the polymer occurs.
As a method of preventing beads from clogging, there are proposed methods of rotating a screen, or applying thereto vibration, as described in, for example, Utility Model Registration No. 3006047, JP-A-63-65959 (xe2x80x9cJP-Axe2x80x9d means unexamined published Japanese patent application), JP-A-10-116512, and JP-A-8-252472. These methods are not to prevent the media itself from reaching the screen, but an attempt to mechanically reduce the probability that the media becomes plugged even though the media have reached the screen. Consequently, it is difficult to say that the effects obtained thereby are satisfactory.
An object of the present invention is to provide a method of efficiently preparing a photographic solid fine-grain dispersion, wherein neither coarse grains nor abrasion materials resulting from media or so on exist, and moreover no aggregate occurs during storage, and which dispersion causes no trouble when the same is coated in a form of the coating film. Another object of the present invention is to provide such a dispersion.
Still another object of the present invention is to provide a silver halide photographic light-sensitive material using such a dispersion.
Other and further objects, features, and advantages of the invention will appear more fully from the following description, taken in connection with the accompanying drawings.